1. Field of the Invention
The present invention relates to a switching valve device, and more particularly to a switching valve device which can selectively obtain at least three states, a state wherein an oil passage provided in a valve casing is cut off only in one direction, a state wherein the oil passage is cut off only in the other direction, and a state wherein the oil passage is cut off in both the directions.
2. Description of the Prior Art
The present assignee has previously proposed (in Japanese Patent Application No. 277,816/84) a switching valve device of the kind as described in which a check valve is provided on a rotary valve body so fitted in a valve casing as to transverse an oil passage in the casing, said rotary body being selectively rotated to three positions, a position wherein the check valve is arranged at a position to cut off the oil passage only in one direction, a position wherein the check valve is arranged at a position to cut off the oil passage only in the other direction, and a position wherein the oil passage is completely cut off.
In the above-proposed switching valve device, since a slight clearance is present between the valve casing and the rotary valve to allow rotation of the valve, it is required to maintain dimensional precision of members at a high level in order to positively obtain a valve closed state, and particularly, when pressure oil is controlled, it is considered that pressure may leak from a high pressure side to a low pressure side through the aforesaid clearance.